When something goes wrong with the processing of a command, the server responds with an error packet. The format is documented in Table 4-9.
Table 4-9. Format of server’s error packet
Offset in the body
Length
Description
0
1
A byte containing 255. The client will always treat a response packet starting with a byte containing 255 as an error message.
1
2
The error code. Low byte first. The field will not be included if the server is talking to a very ancient pre-3.23 client, and the subsequent offsets should be adjusted accordingly in that case.
3
2
Character ‘ # ’ followed by the byte containing the value of the ODBC/JDBC SQL state. Present only in version 4.1 and later.
5 in version 4.1 and later, 3 in 4.0 and earlier
Varies
Zero-terminated text of the error message.
To send an error packet from inside the server, call send_error() , which is defined in sql/protocol.cc in version 4.1 and later, and in sql/net_pkg.cc in version 4.0 and earlier.
EOF Packet
The end-of-file (EOF) packet is used to communicate a number of messages:
EOF) packet is used to communicate a number of messages: The end-of-file (EOF) packet is used to communicate a number of messages:
End-of-field information data in a result set
End-of-row data in a result set
Server acknowledgment of COM_SHUTDOWN
Server reporting success in response to COM_SET_OPTION and COM_DEBUG
Request for the old-style credentials during authentication
The body of an EOF packet always starts with a byte containing decimal 254. In the pre-4.1 era, there was nothing else in the body in addition to this byte. Version 4.1 added another 4 bytes of status fields with the potential of going up to 7 bytes. The format of the version 4.1 EOF body is outlined in Table 4-10.
Table 4-10. Format of server’s EOF packet
Offset in the body
Length
Description
0
1
Byte with the decimal 254
1
2
Number of warnings
3
2
Server status bit mask
The reason for the 7 byte limit in the status bytes area is that the decimal 254 byte followed by an 8 byte string at the beginning of a packet body can have a different meaning: it can specify the number of fields in a result set using the field length format described in the “Data Field ” section, earlier in this chapter.
To send an EOF packet, the server uses send_eof() , which is defined in sql/protocol.cc in 4.1 and later, and in sql/net_pkg.cc in the earlier versions.
